Patent Document 1 discloses a projection-type image display device in which excitation light is scanned to display an image on a fluorescent screen.
The projection-type display device that is disclosed in Patent Document 1 includes a fluorescent screen, a laser module, an optical detection unit, and a feedback adjustment means.
The fluorescent screen includes: a plurality of phosphor stripes formed at a fixed spacing in the in-plane direction; and reference marks that indicate the starting positions of the phosphor stripes and that are arranged on the outside of regions in which these phosphor stripes are provided.
A laser module scans a fluorescent screen with laser beam (excitation light). The optical detection unit detects the laser beam that is reflected by the reference marks. The output signal (detection signal of reference marks) of the optical detection unit is supplied to the feedback adjustment means as a feedback signal.
The feedback adjustment means acquires the timing of irradiation of the laser beam upon reference marks based on the detection signal of the reference marks from the optical detection unit, and based on the acquired irradiation timing, adjusts the light-emission timing of the laser module.
In the above-described projection-type display device, an image is displayed by scanning a fluorescent screen in a direction orthogonal to the phosphor stripes by a laser beam (optical pulse) that is modulated based on a modulation signal to excite the phosphors of each phosphor stripe.
The feedback adjustment means controls the light emission timing of the laser module based on the detection signals of reference marks from the optical detection unit such that the laser beam irradiates the phosphor stripes at the appropriate timing.
Patent Document 2 discloses a fluorescent screen that is used in a projection-type display device.
The fluorescent screen disclosed in Patent Document 2 includes a plurality of phosphor stripes that are formed at a fixed spacing in the in-plane direction and a plurality of stripe dividers that are formed between the phosphor stripes. Each of the plurality of stripe dividers is formed by a diffusive or optically reflective material and reflects a portion of the incident light.
In the projection-type display device that is equipped with the above-described fluorescent screen, an excitation beam is scanned in a direction that crosses the phosphor stripes on the fluorescent screen. Each stripe divider reflects a portion of the incident excitation beam. This reflected light is detected by a photodetector that is provided at a position that faces the scan surface of the fluorescent screen.
The timing of irradiation of each stripe divider by the excitation beam in horizontal scanning is acquired based on the output signal of the photodetector, and by determining the relative positions of the excitation beam with respect to the phosphor stripe based on this irradiation timing, the excitation beam can be irradiated upon the phosphor stripes at the appropriate timing. In this case, each stripe divider functions as a servo-mark for appropriately maintaining the relative position of the excitation beam with respect to the phosphor stripes.
Each stripe divider may be formed by a phosphor material that emits infrared fluorescent light or a phosphor material that emits other light (visible light) for which wavelength differs from that of the visible light (fluorescent light) that is emitted by the phosphor stripes. In this case, a filter that transmits only the fluorescent light (infrared light or other light) from the stripe divider is provided on the light-receiving surface of the photodetector.
Recently, a multi-projection system was provided in which a plurality of the devices disclosed in Patent Document 1 or Patent Document 2 are used as projectors to display images on a fluorescent screen by each scanning with excitation light, and then joining together the images that are displayed by each projector to form a single image.
In order to seamlessly join together the displayed images of each projector in a multi-projection system, the range that each projector displays on the fluorescent screen must be accurately prescribed.
The accurate installation of the fluorescent screens and each of the projectors in alignment with the above-described prescribed display ranges calls for high mounting precision. Achieving high installation precision calls for advanced techniques and places a heavy burden upon workers in the mounting operation.
In addition, in an image display device that displays an image by scanning a fluorescent screen with excitation light, the relative positional relation between the scanning system and fluorescent screen typically undergoes change due to various causes such as the replacement or installation of the fluorescent screen, vibrations or distortion, changes in the environment such as in temperature or humidity, the effect of gravity, or changes that occur with the passage of time. Thus, in order to maintain a state in which the displayed images of each projector are seamlessly joined in a multi-projection system, it is desired that each projector periodically or at arbitrary timings identify the display range of the image that the projector displays and adjust this specified display range to match the above-described prescribed display range.